1. Field of the Invention
The present invention relates to novel ionic purifiers and methods suitable for providing an ultra-high-purity chemical. The ionic purifiers and methods according to this invention have particular applicability to the semiconductor manufacturing industry.
2. Description of the Related Art
In the semiconductor manufacturing industry, a major concern at every stage in the manufacturing process is contamination. Control of contamination is critical to product quality, and an extremely high level of cleanliness and purity in the manufacturing environment is required to obtain acceptable product yield while maintaining profitability. Accordingly, a large fraction of the steps in modern integrated circuit (IC) manufacturing are dedicated to the cleaning of the semiconductor wafers being treated. Such cleanup steps are implemented to remove, for example, organic contaminants, metallic contaminants, photoresist (or inorganic residues thereof), byproducts of etching, native oxides, etc.
A significant source of wafer contamination is impurities in the process chemicals. Because cleanup steps are frequently performed in the manufacturing process and are necessary to maintain product quality, contamination due to cleanup chemistry is very undesirable. Certain chemicals present particular difficulties because they can contain both solid and volatile impurities which can be damaging to electronic components if present during the manufacturing process. Such chemicals can include, for example, ammonia, hydrogen chloride and hydrogen fluoride. The purity levels and compositions of the process chemicals can vary widely, depending on the source as well as the handling method. It is beneficial to reduce the amount of the impurities before the process chemicals are used in modern electronic component production lines.
The high cost and lack of flexibility of current methods for obtaining ultra-high-purity process chemicals contribute considerably to the overall cost of manufacture. Ultra-high-purity process chemicals are typically prepared using distillation processes. However, distillation processes can be impractical due to the cost and process control issues related to such processes.
As an alternative to distillation, process chemicals can be purchased from the limited sources which are able to supply them at an acceptable grade. However, ultra-high-purity process chemicals are generally expensive and typically can only be purchased from a limited number of qualified suppliers.
The use of ionic purifiers for on-site preparation of ultra-high-purity process chemicals has been described, for example, in U.S. Pat. Nos. 5,496,778; 5,722,442; 5,755,934; 5,785,820; 5,846,386; and 5,846,387, the entire contents of which patents are incorporated herein by reference.
FIG. 1 illustrates an ionic purifier 100 of the related art. The ionic purifier 100 includes a vapor inlet 104 which receives a chemical vapor to be purified and directs the vapor into a column 102. A vapor outlet 114 removes a purified chemical vapor from the column 102. A high-purity water inlet 106 introduces high-purity water into the column 102. A recirculation system 108, typically including a pump 110 and a recirculation stream 112, directs liquid that is collected at the lower portion of the column 102 to the upper portion of the column 102. As the chemical vapor to be purified ascends inside the column 102, the descending recirculated liquid countercurrently contacts the vapor, thereby hydrolyzing impurities present therein. The liquid collects at the lower portion of the column 102 and is recirculated to the upper portion of the column 102 for further removal of impurities. A heat exchanger 116 can be used to bring the recirculated liquid to a desired temperature. The ionic purifier 100 can also include a mist removal section 118.
While use of the ionic purifier 100 removes some impurities from the chemical vapor to be purified, it typically does not ensure the removal of species of impurities which have appreciable vapor pressures within the column 102. Most species of impurities are ionized in the aqueous phase and have a negligible vapor pressure above the liquid collected at the lower portion of the column 102, and thus typically do not enter into the vapor outlet 114. However, species with appreciable vapor pressures can be in equilibrium with the purified chemical vapor at the upper portion of the column 102 and can enter into the vapor outlet 114 with the product vapor.
The foregoing description of the related art demonstrates the need for provision of ultra-high-purity chemicals suitable for use in a semiconductor manufacturing process. To meet these requirements and to overcome the disadvantages of the related art, it is an object of the present invention to provide novel ionic purifiers suitable for providing an ultra-high-purity chemical to a semiconductor manufacturing process. It is a further object of the invention to provide novel methods suitable for providing an ultra-high-purity chemical to a semiconductor manufacturing process. The ionic purifiers and methods in accordance with the invention can advantageously be employed on-site at a semiconductor manufacturing facility.
Through the ionic purifiers and methods of the present invention, chemicals can be purified while minimizing or avoiding disadvantages associated with the related art resulting from recirculation of an impure liquid from the lower portion of the purifier to the upper portion thereof.
Other objects and aspects of the present invention will become apparent to one of ordinary skill in the art on a review of the specification, drawings and claims appended hereto.
The foregoing objectives are met by the ionic purifiers and methods of the present invention. According to a first aspect of the present invention, an ionic purifier is provided, suitable for providing an ultra-high-purity chemical to a semiconductor manufacturing process. The ionic purifier comprises:
(a) a vapor inlet for introducing a chemical vapor to be purified into a column;
(b) a high-purity water inlet for continuously introducing high-purity water into the column, wherein the high-purity water contacts the chemical vapor to be purified, thereby forming a purified chemical vapor and contaminated water;
(c) a vapor outlet for removing the purified chemical vapor from the column; and
(d) a liquid outlet for removing the contaminated water from the column.
In accordance with a further aspect of the present invention, a method is provided, suitable for providing an ultra-high-purity chemical to a semiconductor manufacturing process. The method comprises the steps of:
(a) introducing a chemical vapor to be purified into a column;
(b) continuously introducing high-purity water into the column;
(c) contacting the chemical vapor to be purified with the high-purity water, thereby forming a purified chemical vapor and contaminated water;
(d) removing the purified chemical vapor from the column; and
(e) removing the contaminated water from the column.